Cowl induction hood and fuel economy

[ex-tyke]

The fuel economy numbers are in.....
The run to British V8 and back was the first opportunity to gather fuel economy numbers using cowl inducted air rather than underhood air as gathered in previous trips....and it appears that inducting cooler, denser air does result in better fuel economy.
A trip average from many previous years would typically yield 23.5 -24.0 mpg (US) for hwy driving.
Average hwy driving economy from this trip was 25.6 mpg (US).....30.7mpg (Imp)
Average for the complete trip (907 miles/36.33 gal) including any local urban driving was 25.0 mpg (US).......30.0 mpg (Imp)
.....my wallet is feeling happier today.

[MGBV8]

That is amazing, Graham. Your Holley (double pumper, mechanical secondaries, even) equipped 302 is getting the same mileage as my Carter 500 carb'd 215.

 Hmmm.....and the perpetual urban legend is that Holleys don't get good fuel mileage.

[joe_padavano]

Colder, denser air shouldn't increase mileage, if the carb is jetted properly to match the increased mass airflow.  If you didn't change jetting, then the denser air is essentially leaning the mixture.  If the car runs acceptably now, then it was probaby jetted too rich before.

[ex-tyke]

Colder, denser air shouldn't increase mileage, if the carb is jetted properly to match the increased mass airflow. If you didn't change jetting, then the denser air is essentially leaning the mixture. If the car runs acceptably now, then it was probaby jetted too rich before

Joe, what you say is correct - no jet changes were made from previous - fuel economy improvements were strictly the result of switching to cowl inducted air, which would point to a previous rich condition.
I've been thinking of installing an Innovate A/F meter to see exactly how I'm runnning - maybe now's the time!

[MGBV8]

Might want to consider this one for a V8.

[joe_padavano]

If you are suggesting the gauge with two O2 sensors to put one in each manifold, that isn't necessary.  Unless one is using one of the goofball Offy 180 intakes that split the RH/LH sides of the carb, any normal dual plane or single plane intake allows either bank of cylinders to draw from both sides of the carb.  A single O2 sensor on one manifold is sufficient for checking carb jetting.  For example, on the stock 215 intake, cylinders 1, 4, 6, and 7 feed off the LH side of the carb and 2, 3, 5, and 8 from the RH side.  A single O2 sensor in the RH exhaust manifold outlet reads the LH carb jetting in cylinders 4 and 6 and the RH jetting in 2 and 8.  Unless you put an O2 sensor in every single exhaust port to read individual jetting (and have sequential port injection so you can dial in each cylinder), there is no benefit to more than one sensor.

[MGBV8]

Maybe so. but it would bother the heck out of me not being able to monitor each side. I have even seen a switch wired in to flip back & forth.

[Moderator]

I figure you guys will need an O2 sensor when you finally get around to upgrading to EFI;)

EFI installations on v8 engines generally just use one O2 sensor. You can wire a second one and datalog it. Leaving an unused O2 sensor installed isn't recommended because it will tend to get fouled up.

At any rate, an AFR gauge on the instrument panel adds about 10hp to any car.

[roverman]

And a nitrous gauge-adds even more...

[DiDueColpi]

Speaking of useful gauges.
I find that the FFZ gauge in my shop adds power and style to everything that rolls through here.
Generally it's sphere of influence encompasses the entire property.
But when needed it can be focused into a very precise area.
The gauge was conceived during a particularly difficult technician/vehicle interface moment.
And the so FFZ  (f...up Free Zone) gauge was born.
It has served us well ever since.

Live like you mean it.
Fred

[Jim Stabe]

The one between the tach and speedo is the one that adds the most.